Digital cameras comprise a sensor chamber in which is lodged an electronic sensor, such as a charge-coupled device (CCD) sensor or Complementary Metal Oxide Semiconductor (CMOS) sensor, onto which is projected the image of what is seen through the lens of the camera. This sensor can acquire the image projected thereon and convert it into electronic data, which is thereafter forwarded to data processing means provided on the digital camera. The data processing means then converts this electronic data into an image file of known format, such as in JPEG, TIFF or RAW formats, stored thereafter on the memory card of the camera. Of course, this sensor must remain as clean as possible, since impurities deposited thereon can undesirably alter the final image acquired by the camera.
It is inevitable that during normal use of a digital camera, its sensor will become exposed to the atmosphere and its airborne impurities, such as minute airborne dust particles. More particularly, on digital cameras having interchangeable lenses such as digital single-lens reflex (DSLR) cameras, the sensor inevitably becomes exposed to the atmosphere and its impurities whenever the lens is removed from the body of the camera, for example when switching lenses.
Digital camera owners have come up with a number of means to find out if their camera's sensor is covered with contaminants before proceeding with its cleaning. One of them, called the f22 test, consists of shooting pictures while aiming at a lighted backdrop with a uniform background and consistent lighting, while the camera is set on the longest focal length and smallest aperture value. Then, impurities of the sensor surface appear on the photography as blurring spots altering the image. Consequently, this method may require several picture takings and computer application work to bring out the contrast of blur spots on the photography.
It is noted that ordinary magnification without focused light can't help with inspecting the camera sensor surface, since the camera sensor location is deep within the camera frame and ambient light reach this location only minimally. Also, the inspection light can't shine on the sensor directly without causing possibly irreparable damage.